Titanium-copper-iron alloy and associated thixoforming method

ABSTRACT

A titanium alloy that includes about 5 to about 33 percent by weight copper, about 1 to about 8 percent by weight iron, and titanium.

PRIORITY

This application is a divisional of U.S. Ser. No. 15/472,948 filed onMar. 29, 2017.

FIELD

This application relates to titanium alloys and, more particularly, tothixoforming of titanium alloys.

BACKGROUND

Titanium alloys offer high tensile strength over a broad temperaturerange, yet are relatively light weight. Furthermore, titanium alloys areresistant to corrosion. Therefore, titanium alloys are used in variousdemanding applications, such as aircraft components, medical devices andthe like.

Plastic forming of titanium alloys is a costly process. The toolingrequired for plastic forming of titanium alloys must be capable ofwithstanding heavy loads during deformation. Therefore, the tooling forplastic forming of titanium alloys is expensive to manufacture anddifficult to maintain due to high wear rates. Furthermore, it can bedifficult to obtain complex geometries when plastic forming titaniumalloys. Therefore, substantial additional machining is often required toachieve the desired shape of the final product, thereby furtherincreasing costs.

Casting is a common alternative for obtaining titanium alloy productshaving more complex shapes. However, casting of titanium alloys iscomplicated by the high melting temperatures of titanium alloys, as wellas the excessive reactivity of molten titanium alloys with moldmaterials and ambient oxygen.

Accordingly, titanium alloys are some of the most difficult metals to beprocessed in a cost-effective manner. Therefore, those skilled in theart continue with research and development efforts in the field oftitanium alloys.

SUMMARY

In one embodiment, the disclosed titanium alloy includes about 5 toabout 33 percent by weight copper, about 1 to about 8 percent by weightiron, and titanium.

In another embodiment, the disclosed titanium alloy consists essentiallyof about 5 to about 33 percent by weight copper, about 1 to about 8percent by weight iron, and balance titanium.

In yet another embodiment, the disclosed titanium alloy consistsessentially of about 13 to about 33 percent by weight copper, about 3 toabout 5 percent by weight iron, and balance titanium.

In one embodiment, the disclosed method for manufacturing a metallicarticle includes the steps of (1) heating a mass of titanium alloy to athixoforming temperature, the thixoforming temperature being between asolidus temperature of the titanium alloy and a liquidus temperature ofthe titanium alloy, the titanium alloy including copper, iron andtitanium; and (2) forming the mass into the metallic article while themass is at the thixoforming temperature.

In another embodiment, the disclosed method for manufacturing a metallicarticle includes the steps of (1) heating a mass of titanium alloy to athixoforming temperature, the thixoforming temperature being between asolidus temperature of the titanium alloy and a liquidus temperature ofthe titanium alloy, the titanium alloy including about 5 to about 33percent by weight copper, about 1 to about 8 percent by weight iron, andtitanium; and (2) forming the mass into the metallic article while themass is at the thixoforming temperature.

Other embodiments of the disclosed titanium-copper-iron alloy andassociated thixoforming method will become apparent from the followingdetailed description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a phase diagram of a titanium-copper-iron alloy;

FIGS. 2A and 2B are plots of liquid fraction versus temperature forthree example titanium alloys generated assuming equilibrium (FIG. 2A)and Scheil (FIG. 2B) conditions;

FIGS. 3A, 3B and 3C are photographic images depicting themicrostructures versus time (when maintained at 1010° C.) for threeexample titanium alloys, specifically Ti-18Cu-4Fe (FIG. 3A), Ti-20Cu-4Fe(FIG. 3B) and Ti-22Cu-4Fe (FIG. 3C);

FIG. 4 is a flow diagram depicting one embodiment of the disclosedmethod for manufacturing a metallic article;

FIG. 5 is a flow diagram of an aircraft manufacturing and servicemethodology; and

FIG. 6 is a block diagram of an aircraft.

DETAILED DESCRIPTION

Disclosed is a titanium-copper-iron alloy. When the compositional limitsof the copper addition and the iron addition in the disclosedtitanium-copper-iron alloy are controlled as disclosed herein, theresulting titanium-copper-iron alloy may be particularly well-suited foruse in the manufacture of metallic articles by way of thixoforming.

Without being limited to any particular theory, it is believed that thedisclosed titanium-copper-iron alloys are well-suited for use in themanufacture of metallic articles by way of thixoforming because thedisclosed titanium-copper-iron alloys have a relatively broadsolidification range. As used herein, “solidification range” refers tothe difference (ΔT) between the solidus temperature and the liquidustemperature of the titanium-copper-iron alloy, and is highly dependentupon alloy composition. As one example, the solidification range of thedisclosed titanium-copper-iron alloys may be at least about 50° C. Asanother example, the solidification range of the disclosedtitanium-copper-iron alloys may be at least about 100° C. As anotherexample, the solidification range of the disclosed titanium-copper-ironalloys may be at least about 150° C. As another example, thesolidification range of the disclosed titanium-copper-iron alloys may beat least about 200° C. As another example, the solidification range ofthe disclosed titanium-copper-iron alloys may be at least about 250° C.As another example, the solidification range of the disclosedtitanium-copper-iron alloys may be at least about 300° C.

The disclosed titanium-copper-iron alloys become thixoformable whenheated to a temperature between the solidus temperature and the liquidustemperature of the titanium-copper-iron alloy. However, the advantagesof thixoforming are limited when the liquid fraction of thetitanium-copper-iron alloy is too high (processing becomes similar tocasting) or too low (processing becomes similar to plastic metalforming). Therefore, it may be advantageous to thixoform when the liquidfraction of the titanium-copper-iron alloy is between about 30 percentand about 50 percent.

Without being limited to any particular theory, it is further believedthat the disclosed titanium-copper-iron alloys are well-suited for usein the manufacture of metallic articles by way of thixoforming becausethe disclosed titanium-copper-iron alloys achieve a liquid fractionbetween about 30 percent and about 50 percent at temperaturessignificantly below traditional titanium alloy casting temperatures. Inone expression, the disclosed titanium-copper-iron alloys achieve aliquid fraction between about 30 percent and about 50 percent at atemperature less than 1,200° C. In another expression, the disclosedtitanium-copper-iron alloys achieve a liquid fraction between about 30percent and about 50 percent at a temperature less than 1,150° C. Inanother expression, the disclosed titanium-copper-iron alloys achieve aliquid fraction between about 30 percent and about 50 percent at atemperature less than 1,100° C. In another expression, the disclosedtitanium-copper-iron alloys achieve a liquid fraction between about 30percent and about 50 percent at a temperature less than 1,050° C. In yetanother expression, the disclosed titanium-copper-iron alloys achieve aliquid fraction between about 30 percent and about 50 percent at atemperature of about 1,010° C.

In one embodiment, disclosed is a titanium-copper-iron alloy having thecomposition shown in Table 1.

TABLE 1 Element Range (wt %) Cu 5-33 Fe 1-8  Ti Balance

Thus, the disclosed titanium-copper-iron alloy may consist of (orconsist essentially of) titanium (Ti), copper (Cu) and iron (Fe).

Those skilled in the art will appreciate that various impurities, whichdo not substantially affect the physical properties of the disclosedtitanium-copper-iron alloy, may also be present, and the presence ofsuch impurities will not result in a departure from the scope of thepresent disclosure. For example, the impurities content of the disclosedtitanium-copper-iron alloy may be controlled as shown in Table 2.

TABLE 2 Impurity Maximum (wt %) O 0.25 N 0.03 Other Elements, Each 0.10Other Elements, Total 0.30

The copper addition to the disclosed titanium-copper-iron alloyincreases the liquid fraction at a given temperature. Therefore, withoutbeing limited to any particular theory, it is believed that the copperaddition contributes to the thixoformability of the disclosedtitanium-copper-iron alloy.

As shown in Table 1, the compositional limits of the copper addition tothe disclosed titanium-copper-iron alloy range from about 5 percent byweight to about 33 percent by weight. In one variation, thecompositional limits of the copper addition range from about 13 percentby weight to about 33 percent by weight. In another variation, thecompositional limits of the copper addition range from about 15 percentby weight to about 30 percent by weight. In another variation, thecompositional limits of the copper addition range from about 17 percentby weight to about 25 percent by weight. In yet another variation, thecompositional limits of the copper addition range from about 18 percentby weight to about 22 percent by weight.

Iron is a strong β-stabilizer, but can increase density and causeembrittlement. Therefore, without being limited to any particulartheory, it is believed that the iron addition retains the Ti-β phaseduring cooling, but without an excessive density increase and withoutcausing significant embrittlement.

As shown in Table 1, the compositional limits of the iron addition tothe disclosed titanium-copper-iron alloy range from about 1 percent byweight to about 8 percent by weight. In one variation, the compositionallimits of the iron addition range from about 2 percent by weight toabout 7 percent by weight. In another variation, the compositionallimits of the iron addition range from about 3 percent by weight toabout 6 percent by weight. In another variation, the compositionallimits of the iron addition range from about 3 percent by weight toabout 5 percent by weight. In yet another variation, iron is present ata concentration of about 4 percent by weight.

Example 1 Ti-13-33Cu-4Fe

One general, non-limiting example of the disclosed titanium-copper-ironalloy has the composition shown in Table 3.

TABLE 3 Element Concentration (wt %) Cu 13-33 Fe 4 Ti Balance

Referring to the phase diagram of FIG. 1, specifically to thecross-hatched region of FIG. 1, the disclosed Ti-13-33Cu-4Fe alloy has arelatively low solidus temperature (around 1,000° C.) and a relativelybroad solidification range. Therefore, the disclosed Ti-13-33Cu-4Fealloy is well-suited for thixoforming.

Example 2 Ti-18Cu-4Fe

One specific, non-limiting example of the disclosed titanium-copper-ironalloy has the following nominal composition:

Ti-18Cu-4Fe

and the measured composition shown in Table 4.

TABLE 4 Element Concentration (wt %) Ti Balance Cu 17.7 ± 0.6  Fe 4.0 ±0.1 O 0.155 ± 0.006 N 0.008 ± 0.001

PANDAT™ software (version 2014 2.0) from CompuTherm LLC of Middleton,Wis., was used to generate liquid fraction versus temperature data forthe disclosed Ti-18Cu-4Fe alloy, assuming both equilibrium conditionsand Scheil conditions. The results are shown in FIGS. 2A (equilibriumconditions) and 2B (Scheil conditions). Based on the data from FIG. 2A(equilibrium conditions), the disclosed Ti-18Cu-4Fe alloy has a solidustemperature of about 1,007° C. and a liquidus temperature of about1,345° C., with a solidification range of about 338° C. (364° C. usingScheil conditions/FIG. 2B).

Referring to FIG. 3A, the disclosed Ti-18Cu-4Fe alloy was heated to1,010° C.—a temperature between the solidus and liquidus temperatures(i.e., a thixoforming temperature)—and micrographs were taken at 0seconds, 60 seconds, 300 seconds and 600 seconds. The micrographs showhow the disclosed Ti-18Cu-4Fe alloy has a globular microstructure at1,010° C. that becomes increasingly globular over time. Therefore, thedisclosed Ti-18Cu-4Fe alloy is particularly well-suited forthixoforming.

Example 3 Ti-20Cu-4Fe

Another specific, non-limiting example of the disclosedtitanium-copper-iron alloy has the following nominal composition:

Ti-20Cu-4Fe

and the measured composition shown in Table 5.

TABLE 5 Element Concentration (wt %) Ti Balance Cu 19.5 ± 0.5  Fe 4.0 ±0.1 O 0.166 ± 0.010 N 0.008 ± 0.001

PANDAT™ software (version 2014 2.0) was used to generate liquid fractionversus temperature data for the disclosed Ti-20Cu-4Fe alloy, assumingboth equilibrium conditions and Scheil conditions. The results are shownin FIGS. 2A (equilibrium conditions) and 2B (Scheil conditions). Basedon the data from FIG. 2A (equilibrium conditions), the disclosedTi-20Cu-4Fe alloy has a solidus temperature of about 999° C. and aliquidus temperature of about 1,309° C., with a solidification range ofabout 310° C. (329° C. using Scheil conditions/FIG. 2B).

Referring to FIG. 3B, the disclosed Ti-20Cu-4Fe alloy was heated to1,010° C.—a temperature between the solidus and liquidus temperatures(i.e., a thixoforming temperature)—and micrographs were taken at 0seconds, 60 seconds, 300 seconds and 600 seconds. The micrographs showhow the disclosed Ti-20Cu-4Fe alloy has a globular microstructure at1,010° C. that becomes increasingly globular over time. Therefore, thedisclosed Ti-20Cu-4Fe alloy is particularly well-suited forthixoforming.

Example 4 Ti-22Cu-4Fe

Yet another specific, non-limiting example of the disclosedtitanium-copper-iron alloy has the following nominal composition:

Ti-22Cu-4Fe

and the measured composition shown in Table 6.

TABLE 6 Element Concentration (wt %) Ti Balance Cu 21.5 ± 0.5  Fe 4.0 ±0.1 O 0.176 ± 0.013 N 0.008 ± 0.001

PANDAT™ software (version 2014 2.0) was used to generate liquid fractionversus temperature data for the disclosed Ti-22Cu-4Fe alloy, assumingboth equilibrium conditions and Scheil conditions. The results are shownin FIGS. 2A (equilibrium conditions) and 2B (Scheil conditions). Basedon the data from FIG. 2A (equilibrium conditions), the disclosedTi-22Cu-4Fe alloy has a solidus temperature of about 995° C. and aliquidus temperature of about 1,271° C., with a solidification range ofabout 276° C. (290° C. using Scheil conditions/FIG. 2B).

Referring to FIG. 3C, the disclosed Ti-22Cu-4Fe alloy was heated to1,010° C.—a temperature between the solidus and liquidus temperatures(i.e., a thixoforming temperature)—and micrographs were taken at 0seconds, 60 seconds, 300 seconds and 600 seconds. The micrographs showhow the disclosed Ti-22Cu-4Fe alloy has a globular microstructure at1,010° C. that becomes increasingly globular over time. Therefore, thedisclosed Ti-22Cu-4Fe alloy is particularly well-suited forthixoforming.

Accordingly, discloses are titanium-copper-iron alloys that arewell-suited for thixoforming. Also, disclosed are methods formanufacturing a metallic article, particularly a titanium alloy article,by way of thixoforming.

Referring now to FIG. 4, one embodiment of the disclosed method formanufacturing a metallic article, generally designated 10, may begin atBlock 12 with the selection of a titanium alloy for use as a startingmaterial. For example, the selection of a titanium alloy (Block 12) mayinclude selecting a titanium-copper-iron alloy having the compositionshown in Table 1, above.

At this point, those skilled in the art will appreciate that selectionof a titanium alloy (Block 12) may include selecting a commerciallyavailable titanium alloy or, alternatively, selecting a non-commerciallyavailable titanium alloy. In the case of a non-commercially availabletitanium alloy, the titanium alloys may be custom made for use in thedisclosed method 10.

As is disclosed herein, the solidification range may be oneconsideration during selection (Block 12) of a titanium alloy. Forexample, selection of a titanium alloy (Block 12) may include selectinga titanium-copper-iron alloy having a solidification range of at least50° C., such as at least 100° C., or at least 150° C., or at least 200°C. or at least 250° C., or at least 300° C.

As is also disclosed herein, the temperature at which a liquid fractionbetween about 30 percent and about 50 percent is achieved may be anotherconsideration during selection (Block 12) of a titanium alloy. Forexample, selection of a titanium alloy (Block 12) may include selectinga titanium-copper-iron alloy that achieves a liquid fraction betweenabout 30 percent and about 50 percent at a temperature less than 1,200°C., such as a temperature less than 1,150° C., or a temperature lessthan 1,100° C., or a temperature less than 1,050° C.

At Block 14, a mass of the titanium alloy may be heated to athixoforming temperature (i.e., a temperature between the solidus andliquidus temperatures of the titanium alloy). In one particularimplementation, the mass of the titanium alloy may be heated to aparticular thixoforming temperature, and the particular thixoformingtemperature may be selected to achieve a desired liquid fraction in themass of the titanium alloy. As one example, the desired liquid fractionmay be about 10 percent to about 70 percent. As another example, thedesired liquid fraction may be about 20 percent to about 60 percent. Asyet example, the desired liquid fraction may be about 30 percent toabout 50 percent.

At Block 16, the mass of the titanium alloy may optionally be maintainedat the thixoforming temperature for a predetermined minimum amount oftime prior to proceeding to the next step (Block 18). As one example,the predetermined minimum amount of time may be about 10 seconds. Asanother example, the predetermined minimum amount of time may be about30 seconds. As another example, the predetermined minimum amount of timemay be about 60 seconds. As another example, the predetermined minimumamount of time may be about 300 seconds. As yet another example, thepredetermined minimum amount of time may be about 600 seconds.

At Block 18, the mass of the titanium alloy may be formed into ametallic article while the mass is at the thixoforming temperature.Various forming techniques may be used, such as, without limitation,casting and molding.

Accordingly, the disclosed titanium-copper-iron alloy and associatedthixoforming method may facilitate the manufacture of net shape (or nearnet shape) titanium alloy articles at temperatures that aresignificantly lower than traditional titanium casting temperatures, andwithout the need for the complex/expensive tooling typically associatedwith plastic forming of titanium alloys. Therefore, the disclosedtitanium-copper-iron alloy and associated thixoforming method have thepotential to significantly reduce the cost of manufacturing titaniumalloy articles.

Examples of the disclosure may be described in the context of anaircraft manufacturing and service method 100, as shown in FIG. 5, andan aircraft 102, as shown in FIG. 6. During pre-production, the aircraftmanufacturing and service method 100 may include specification anddesign 104 of the aircraft 102 and material procurement 106. Duringproduction, component/subassembly manufacturing 108 and systemintegration 110 of the aircraft 102 takes place. Thereafter, theaircraft 102 may go through certification and delivery 112 in order tobe placed in service 114. While in service by a customer, the aircraft102 is scheduled for routine maintenance and service 116, which may alsoinclude modification, reconfiguration, refurbishment and the like.

Each of the processes of method 100 may be performed or carried out by asystem integrator, a third party, and/or an operator (e.g., a customer).For the purposes of this description, a system integrator may includewithout limitation any number of aircraft manufacturers and major-systemsubcontractors; a third party may include without limitation any numberof venders, subcontractors, and suppliers; and an operator may be anairline, leasing company, military entity, service organization, and soon.

As shown in FIG. 6, the aircraft 102 produced by example method 100 mayinclude an airframe 118 with a plurality of systems 120 and an interior122. Examples of the plurality of systems 120 may include one or more ofa propulsion system 124, an electrical system 126, a hydraulic system128, and an environmental system 130. Any number of other systems may beincluded.

The disclosed titanium-copper-iron alloy and associated thixoformingmethod may be employed during any one or more of the stages of theaircraft manufacturing and service method 100. As one example,components or subassemblies corresponding to component/subassemblymanufacturing 108, system integration 110, and or maintenance andservice 116 may be fabricated or manufactured using the disclosedtitanium-copper-iron alloy and associated thixoforming method. Asanother example, the airframe 118 may be constructed using the disclosedtitanium-copper-iron alloy and associated thixoforming method. Also, oneor more apparatus examples, method examples, or a combination thereofmay be utilized during component/subassembly manufacturing 108 and/orsystem integration 110, for example, by substantially expeditingassembly of or reducing the cost of an aircraft 102, such as theairframe 118 and/or the interior 122. Similarly, one or more of systemexamples, method examples, or a combination thereof may be utilizedwhile the aircraft 102 is in service, for example and withoutlimitation, to maintenance and service 116.

The disclosed titanium-copper-iron alloy and associated thixoformingmethod is described in the context of an aircraft; however, one ofordinary skill in the art will readily recognize that the disclosedtitanium-copper-iron alloy and associated thixoforming method may beutilized for a variety of applications. For example, the disclosedtitanium-copper-iron alloy and associated thixoforming method may beimplemented in various types of vehicle including, for example,helicopters, passenger ships, automobiles, marine products (boat,motors, etc.) and the like. Various non-vehicle applications, such asmedical applications, are also contemplated.

Although various embodiments of the disclosed titanium-copper-iron alloyand associated thixoforming method have been shown and described,modifications may occur to those skilled in the art upon reading thespecification. The present application includes such modifications andis limited only by the scope of the claims.

What is claimed is:
 1. A titanium alloy comprising: about 5 to about 33percent by weight copper; about 1 to about 8 percent by weight iron; andbalance titanium and impurities.
 2. The titanium alloy of claim 1wherein said copper is present at about 13 to about 33 percent byweight.
 3. The titanium alloy of claim 1 wherein said copper is presentat about 15 to about 30 percent by weight.
 4. The titanium alloy ofclaim 1 wherein said copper is present at about 17 to about 25 percentby weight.
 5. The titanium alloy of claim 1 wherein said copper ispresent at about 18 to about 22 percent by weight.
 6. The titanium alloyof claim 1 wherein said iron is present at about 2 to about 7 percent byweight.
 7. The titanium alloy of claim 1 wherein said iron is present atabout 3 to about 6 percent by weight.
 8. The titanium alloy of claim 1wherein said iron is present at about 3 to about 5 percent by weight. 9.The titanium alloy of claim 1 wherein said iron is present at about 4percent by weight.
 10. The titanium alloy of claim 1 wherein: saidcopper is present at about 13 to about 33 percent by weight, and saidiron is present at about 3 to about 6 percent by weight.
 11. Thetitanium alloy of claim 1 wherein: said copper is present at about 15 toabout 30 percent by weight, and said iron is present at about 3 to about5 percent by weight.
 12. The titanium alloy of claim 1 wherein: saidcopper is present at about 17 to about 25 percent by weight, and saidiron is present at about 3 to about 5 percent by weight.
 13. Thetitanium alloy of claim 1 wherein oxygen is present as an impurity at aconcentration of at most about 0.25 percent by weight.
 14. The titaniumalloy of claim 1 wherein nitrogen is present as an impurity at aconcentration of at most about 0.03 percent by weight.
 15. The titaniumalloy of claim 1 consisting of said copper, said iron and said titanium.16. The titanium alloy of claim 1 having a solidus temperature and aliquidus temperature, wherein a difference between said solidustemperature and said liquidus temperature is at least 50° C.
 17. Thetitanium alloy of claim 1 having a solidus temperature and a liquidustemperature, wherein a difference between said solidus temperature andsaid liquidus temperature is at least 50° C.
 18. The titanium alloy ofclaim 1 having a solidus temperature and a liquidus temperature, whereina difference between said solidus temperature and said liquidustemperature is at least 100° C.
 19. The titanium alloy of claim 1 havinga solidus temperature and a liquidus temperature, wherein a differencebetween said solidus temperature and said liquidus temperature is atleast 150° C.
 20. The titanium alloy of claim 1 having a solidustemperature and a liquidus temperature, wherein a difference betweensaid solidus temperature and said liquidus temperature is at least 200°C.